1. Field of the Invention
The present invention relates to a coal-fired steam generator that has a water-steam circulation in a low pressure-heat carrier-circulation which, via a heater that is disposed in the flue gas flow of the steam generator and that has at least one heat transfer surface, absorbs heat from the flue gas flow and conveys this heat to a process that utilizes heat, especially in conjunction with a coal-combination combined cycle unit having a steam turbine connected in the water-steam circulation and a gas turbine process.
In the present application, "low pressure-heat carrier" refers to a heat carrier that, in contrast to steam, can be utilized at lower pressures to convey heat. Included are helium, metals such as sodium, as well as oils and salts that at low pressures remain liquid until very high temperatures are reached, so that they can be conveyed via pumps.
2. Description of the Prior Art
VGB Kraftwerkstechnik, 65.sup.th year, issue 6 (1985), pages 545-557, especially FIGS. 10 and 11 on page 550, discloses a steam generator where the low pressure-heat carrier-circulation is a sodium circulation. Since the heat or the sodium circulation is released in the firing of the steam generator, which follows the gas turbine in the combined cycle, there exists the possibility for accommodating the sodium-steam heater in the steam generator in such a way that it is disposed at a location that for it is advantageous, whereas those heat transfer surfaces of the steam generator that are greatly stressed due to the combustion are water cooled as previously. This reduces the stress on the high-alloy materials required for the construction of the sodium heater.
An object of the present invention is to provide a particularly advantageous location for the arrangement of the low pressure heat exchanger.